Conventional emulsifying agents or solubilizing agents are various compounds, for example, ethylene oxide-based nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene polyhydric alcohol fatty acid esters, and polyoxyethylene alkylphenyl ethers, and ionic surfactants. In the field of foods, surfactants which are highly safe, such as sorbitan fatty acid esters, sucrose fatty acid esters, polyglycerol fatty acid esters, and polyglycerol condensed ricinoleates have been known. Among them, the polyglycerol fatty acid esters are the most useful surfactant because the polyglycerol fatty acid esters have high safety to human body and environment and the polyglycerol fatty acid esters can be obtained in various kinds of compositions, thereby giving high versatility.
Regarding the polyglycerol fatty acid esters, a polyglycerol fatty acid ester in which degree of polymerization and HLB of the polyglycerol are defined has been conventionally reported (see Patent Publication 1). However, a polyglycerol fatty acid ester in which a ratio of primary hydroxyl groups is defined has not been reported.
On the other hand, a polyglycerol used as a raw material for a polyglycerol fatty acid ester can be generally obtained by subjecting a glycerol used as a raw material to dehydration-condensation in the presence of a catalyst such as sodium hydroxide while heating, and purifying the reaction mixture by distillation, decolorization, deodorization, ion-exchange resin treatment, or the like, as occasion demands. The end point of the dehydration-condensation is usually determined by the measurement results of its hydroxyl value.
Patent Publication 1: Japanese Patent Laid-Open No. Hei 6-192065